FBG传感器进行PHC管桩负摩阻力监测的研究

Monitoring negative skin frictions on PHC pipe piles using FBG sensors

目前,针对实际工程中预应力高强混凝土(PHC)管桩的负摩阻力现场实测研究几乎未见报道。为了揭示PHC管桩的负摩阻力特性,填补此类桩现场负摩阻力量测试验的空白,研究光纤布拉格光栅(FBG)传感器在PHC管桩桩身上的安装工艺及保护措施,并对某建筑基础的4根承受新近填土产生的负摩擦阻力作用的工程桩桩身应变进行长达21个月的监测,分析在上部结构荷载以及负摩阻力共同作用下桩身轴力的分布形式及其变化特征。试验结果表明:PHC工程桩负摩阻力下拉荷载的实测值显著大于我国现行《建筑桩基技术规范》(JGJ94-2008)理论计算值,说明现行理论方法尚有待改进;在软硬分布不均的地层中,负摩阻力和正摩阻力可能交替出现,理论计算中如何考虑这类情况值得研究;沥青涂层的涂抹质量和如何避免施工破坏是确保其能否有效降低工程桩负摩阻力的关键。

At present,there are almost no reports on the field measurement of the prestressed high-strength concrete（PHC） pipe pile subjected to negative skin friction. To reveal the characteristics of negative skin friction on PHC pile piles,the measures of installation of and protection to the fiber Bragg grating sensors（FBG） on the PHC pipe piles were studied and the strains of 4 piles of a building foundation subjected to negative skin frictions induced by the recent soil filling were monitored for 21 months. The axial forces of the piles were deduced and their variation curves were plotted. The distribution and variation features of the axial forces of the piles under the loads from the superstructure and the negative skin frictions were analyzed. The measured values of the drag loads induced by the negative skin frictions on the PHC piles were notably greater than the values calculated according to the current Chinese code-Technical Code for Building Pile Foundation（JGJ94-2008）,indicating that the current theoretical method still needs to be improved. In the strata with non-uniformly distributed soft and stiff layers,the negative skin and positive skin frictions might occur alternately and how to consider this kind of circumstance in theoretical calculations is worth studying. The quality of and avoiding the construction damage to the asphalt coating are the key to ensure the effective reduction of the negative skin friction.